The instant invention relates to the production of low BTU fuel for use in a combined cycle power plant. In order to maximize the efficiency of the gas turbine component in such an arrangement, it is preferred that the fuel gas supplied to the combustor thereof be hot and be saturated with water vapor. Therefore, it has been proposed to subject a gasifier product gas stream, which has been cooled to accommodate the cleanup sequence, to a reheat and resaturation step prior to entry thereof into the combustor.
The reheat and resaturation step so proposed would be accomplished in a packed tower or tray tower by direct contact between the cool, clean gas and a hot, water-containing liquid stream, generated in preceding process steps.
Unfortunately, the liquid stream contains particulates and dissolved salts. Direct contact between the liquid and gas streams as proposed would result in the entrainment of droplets in the product gas stream in normal operation and, in the event that foaming occurs in the tower, such carryover would be inevitable. The entrainment of droplets in the fuel gas will result in the transfer of such droplets to the combustor and this in turn will cause undesirable flame conditions (e.g., a luminous flame which results in overheating of the combustor lining) and such droplets may contain alkali metal salts, which pose problems of corrosion of the hot gas path including the transition piece and turbine section.
The term "microporous" as used in describing the barrier employed herein refers to conditions of porosity such that the cross-sections of the individual pores have areas equivalent to circles having diameters of less than about 1 micrometer and flow communication through the barrier occurs via more than about 5% of the pores (e.g., through interconnection of the pores).
Percentages used herein to describe water vapor content of a gas stream refer to percent by volume.